1. Field of the Invention
The present invention relates to a so-called clamshell type image forming apparatus utilized for a printer, copying machine and the like.
2. Description of the Prior Art
A clamshell type image forming apparatus, disclosed in, for example, U.S. Pat. No. 4,588,280, is, generally, divided into an upper structure including an optical system, process cartridge and associated elements and a lower structure including a paper feed cassette and associated elements with a conveying path of recording paper interposed therebetween. The apparatus is and constructed such that the upper structure is supported so as to close and open vertically against the lower structure like a clamshell. In such a clamshell type image forming apparatus, it is advantageous in maintenance and checking and when conveying troubles on recording paper have to be responded immediately.
In addition, U.S. Pat. No. 4,598,993 discloses a process cartridge having a developing unit.
In the process cartridge included in the upper structure of the clamshell type image forming apparatus, usually, a sliding construction in which it can be engaged and disengaged lengthwise along a sliding guide member is adopted. In such a construction, however, since the supporting mechanisms such as the sliding guide member became complicated and the weight of the upper structure becomes heavier, the supporting mechanism itself must be made large. Moreover, a positioning accuracy of an optical system and photoreceptor which constitutes the process cartridge is apt to deteriorate and thus it is difficult to maintain proper image definition for a long period of time.
Also, in the clamshell type image forming apparatus wherein the developing unit is constructed separate from the process cartridge and the developing unit is disposed in the lower structure, though the developing unit and an image holding medium are positioned when the upper structure is brought to the close position, at this time, there is the possibility that the image holding medium and the developing unit will contact each other and the image holding medium may break due to the impact occurred thereat, or in order to avoid such problem, the supporting construction of the developing unit becomes complicated.